Highly potent biologically active agents, such as, for example, anticancer drugs and genes, can kill healthy and diseased cells indiscriminately. Therefore, if these biologically active agents are to be most effective against their intended cellular targets without causing adverse patient reactions and/or toxicity, a macromolecular delivery vehicle should transport the agents to a specific desired site.
Complex polymers can be prepared with controlled functionality and architecture for delivery of biologically active agents. However, the biological activities (e.g., toxicity and efficacy) of the biologically active agents can vary widely depending on the molecular weight and surface structure of the polymeric delivery vector. It can be difficult to prepare a complex polymer of a desired size that responds in a predictable way to a particular drug and/or gene, and it is difficult to fully utilize the functionality of such compounds.
The hydrophobic core or the hydrophilic shell of micelles made from amphiphilic copolymers can enclose and immobilize biologically active agents, protecting the agents from uptake by the immune system, and enhancing their bioavailability and biodistribution. In addition, a biological signal can be chemically conjugated onto the surface of the micelles to target specific tissues or cells within the body. However, currently available micelles are difficult to make in a desired size, structurally dynamic, and have low critical micelle concentrations. As a result, their capacity to load and transport biologically active agents can be limited.